The shut-off/equalizing valve of the present invention is used in a system for positioning large devices such as air registers of the type used in boilers to change the amount of combustion air. In an "automatic" position the shut-off/equalizing valve allows air to flow unrestricted to the positioner. In the event that the device which the positioner is controlling must be operated manually, the shut-off/equalizing valve can be placed in a "manual" position. In this position the supply air to the positioner is shut off and the positioner's two outputs are connected together. This unloads the device controlled by the positioner so that it can be manually adjusted.
The prior art construction of the shut-off/equalizing valve includes multiple parts, requiring bonding a two-piece valve core together, installing replaceable O-rings, and requires custom assembly in the form of shimming to assure the correct compression of the O-rings. Surface finish in O-ring seal cavities and on other moving parts requires secondary machining operations in order to avoid premature wear. Also, O-rings are subject to rolling and twisting within their cavities, which also can produce premature wear.